Photography means "writing with light". Writing with light opens two worlds, one about reproducing the reality (what we see, what all of us see); one is about writing our own reality, something that not everybody captures, something that we have in our heart and in our inner sight.
This means that combining several elements, light off course, aperture, time (the time needed for the light to pass through the objective and imprinting the picture on the film), white balance (meaning that particular white - thanks Ansel); combining all those elements, we get what we want.
This is not a course, but simply mentioning the fact that photography is a metaphor of life. Combining all the elements that we've at our disposal we try to get what we want. Not always we've enough time, not always we've the right aperture (or attitude), not always we've the right "light", not always we've the right topic or subject, being real or imaginative. Sometimes, even combining those elements with perfection, the picture is blurred, or not exactly what we wanted to get; that's why, more than combining the elements and know exactly what we want, there's another element, that we cannot control, fate or fortune.
Pictures, all the pictures, are the portrait of a world, but also of people, like that thoughtful faces, melancholic and happy. Those are not the result of what we look for, but of what we find, what we discover.
This is the beauty of the pictures. Pictures are not abstract ideas or inventions. They have something concrete. The world has been exactly like that, at least for that bit.